This invention generally relates to inkjet printers and methods and more particularly relates to an inkjet printer cartridge and method of assembling same, the cartridge being adapted to avoid chemical interaction between ink stored in the cartridge and a seal sealing the cartridge.
An inkjet printer produces images on a recording medium by ejecting ink droplets onto the recording medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the ability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
More specifically, an ink jet printer comprises an inkjet printer cartridge that includes a plurality of ink ejection chambers and a plurality of ink ejection orifices in communication with respective ones of the ink ejection chambers. At every orifice a heat actuated ink ejector, such as found in thermal ink jet printers, is used to produce an ink droplet. In such thermal ink jet printers, a heater locally heats the ink body and a quantity of the ink phase changes into a gaseous steam bubble. The steam bubble raises the internal ink pressure sufficiently for an ink droplet to be expelled through the ink ejection orifice and toward the recording medium. Thermal inkjet printers are well-known and are discussed, for example, in U.S. Pat. Nos. 4,500,895 to Buck, et al.; U.S. Pat. No. 4,794,409 to Cowger, et al.; U.S. Pat. No. 4,771,295 to Baker, et al.; U.S. Pat. No. 5,278,584 to Keefe, et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), the disclosures of which are all hereby incorporated by reference.
The inkjet printer cartridge itself may be a carriage mounted printer cartridge that reciprocates transversely with respect to the recording medium (i.e., across the width of the recording medium) as a controller connected to the printer cartridge selectively fires individual ones of the ink ejection chambers. Each time the printer cartridge traverses the recording medium, a swath of information is printed on the recording medium. After printing the swath of information, the printer advances the recording medium the width of the swath and the printer cartridge prints another swath of information in the manner mentioned immediately hereinabove. This process is repeated until the desired image is printed on the recording medium. Alternatively, the printer cartridge may be a page-width printer cartridge that is stationary and that has a length sufficient to print across the width of the recording medium. In this case, the recording medium is moved continually and normal to the stationary printer cartridge during the printing process.
Inks useable with thermal inkjet printers, whether those printers have carnage-mounted or page-width printer cartridges, are specially formulated to provide suitable images on the recording medium. Such inks typically include a colorant, such as a pigment or dye, and an aqueous liquid, such as water, and/or a low vapor pressure solvent. More specifically, the ink is a liquid composition comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives and other components. Moreover, the solvent or carrier liquid may be water alone or water mixed with water miscible solvents such as polyhydric alcohols, or organic solvents. Various liquid ink compositions are disclosed, for example, by U.S. Pat. No. 4,381,946 titled xe2x80x9cInk Composition For Ink-Jet Recordingxe2x80x9d issued May 3, 1983 in the name of Masafumi Uehara, et al.
The printer cartridge includes a central cavity that is filled with ink of a predetermined color during manufacture of the cartridge. Composition of the cartridge walls may comprise polyethylene naphthalate, which is known to be resistant to corrosive effects of ink materials. The terminology xe2x80x9ccorrosive effectxe2x80x9d means chemical deterioration when the ink comes in contact with a material. The printer cartridge also includes an inlet aperture in communication with the cavity for allowing the cavity to be filled with the ink. Disposed in the inlet aperture is an elastomeric seal that seals the aperture, so that the ink does not exit the cavity through the aperture after being filled with ink. The composition of the elastomeric seal may comprise constituents, such as silicone rubber with zinc oxide and stearic acid as additives. An exemplary inkjet printer cartridge is disclosed more fully, for example, by U.S. Pat. No. 6,113,229 titled xe2x80x9cInterchangeable Fluid Interconnect Attachment And Interfacexe2x80x9d issued Sept. 5, 2000, in the name of Max Stephen Gunther, et al. and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated by reference.
As a step in manufacture of the cartridge, an adhesive tape is placed over the exterior of the ink ejection orifices to prevent ink leaking from the orifices during packaging, shipment and storage of the newly manufactured cartridge. The composition of the adhesive tape exposed to the ink adjacent to the ink ejection orifice may comprise zinc stearate as a constituent. After manufacture, the cartridge is packaged and typically shipped to a retailer or distributor of such cartridges whereupon the cartridge may be stored for a period of time, such as several months, prior to delivery to an end user of the cartridge. Of course, before placing the cartridge in the printer carriage, the end user manually removes the adhesive tape covering the ink ejection orifices, so that ink can be ejected from the cartridge during the printing process.
During printing, the ink in the cartridge cavity is gradually depleted. When sufficiently depleted, the cartridge is discarded and replaced with another cartridge containing ink. However, the heat actuated ink ejector typically remains operable even after depletion of the ink in the cartridge. In other words, the heat actuated ink ejector has useful operational life remaining although the ink in the cartridge is depleted. This has given rise to an after-market in which used cartridges are refilled, resold and re-used. This has also given rise to development of inkjet printer systems using an external ink supply reservoir connectable to the depleted cartridge for refilling the cartridge by means of a hollow ink supply needle. The needle is capable of piercing the seal to inject ink into the cavity formed in the cartridge.
However, it has been observed that during storage of the newly manufactured ink cartridge, the ink in the cavity may chemically interact with the zinc oxide and stearic acid constituents of the seal that seals the cartridge cavity. Over time, the ink leaches the zinc oxide and stearic acid from the seal to form zinc stearate crystals in the ink in the cavity. These zinc stearate crystals then migrate to the ink ejection orifices to clog or block the ink ejection orifices. However, the precise mechanism by which the zinc stearate crystals form is not completely understood. In this regard, zinc stearate may instead remain in solution (i.e., dissolved) in the ink in the cavity and only form crystals on the adhesive tape covering the orifices. In this instance, the crystals may accumulate in the orifices to clog or block the orifices. In any event, it is undesirable to block the ink ejection orifices. It is undesirable to block the ink ejection orifices because blocking the ink ejection orifices interferes with proper ejection of ink drops during printing. Thus, it would be desirable to avoid chemical interaction between the ink and the seal during shipment and prolonged storage. Consequently, a problem in the art is chemical interaction between the ink and the seal.
Therefore, what is needed is an inkjet printer cartridge adapted to avoid chemical interaction between ink stored in the cartridge and a seal sealing the cartridge.
In its broad form, the present invention comprises a printer ink cartridge comprising a shell defining a cavity and a port; a seal spanning the port; and a barrier interposed between the cavity and the seal for isolating the cavity from the seal. In this manner, the inkjet printer cartridge is adapted to avoid chemical interaction between ink stored in the cartridge and the seal sealing the cartridge.
According to an aspect of the present invention, the printer ink cartridge comprises a shell formed by a wall defining a cavity in the shell for storing ink. Disposed in the shell is a print head for ejecting ink drops through corresponding ink ejection orifices formed in the shell. These ink drops are ejected during printing to form an image on a recording medium. The shell also defines an inlet port through the wall for allowing access to the cavity. An elastomeric seal or septum is matingly disposed in the port for sealing the port, the septum having a first surface and a second surface and a slit centrally therethrough extending from the first surface to the second surface. The purpose of the slit is to sealably receive an ink supply needle during refilling of the cartridge.
However, during prolonged shipment and storage of a newly manufactured cartridge, the ink in the cavity may chemically interact with the septum to form crystals that accumulate in the ink ejection orifices to block the orifices. Accumulation of such crystals in the ink ejection orifices is undesirable because such accumulation of crystals interferes with proper ejection of ink droplets during printing.
Therefore, according to the invention, a movable barrier is interposed between the cavity and the septum during manufacture of the cartridge. The barrier covers the port for isolating the ink in the cavity from the septum in order to avoid chemical interaction between the ink and the septum. The barrier preferably remains covering the port until it is required to refill the cartridge with ink. That is, during refilling of the cartridge, the ink supply needle pushes the barrier after the needle is received through the slit in the septum. The barrier moves as the needle pushes the barrier. As the barrier moves, it will move away from the port in order to uncover the port. At this point, the needle supplies refill ink through the uncovered port and into the cartridge.
According to the invention, a first embodiment barrier comprises a plug. The plug comprises a post extending into the port. A flange surrounds the post and is integrally attached thereto for covering the port. As the needle is received through the slit of the septum during the refilling process, the needle will encounter and push the post. The plug, comprising the post and integrally attached flange, will then be expelled from the port and fall to the bottom of the cartridge cavity as the needle pushes the post. This allows the needle access to the cavity for refilling the cavity with ink.
According to a second embodiment barrier, the previously mentioned plug includes a flange that has an annular recessed portion therein of reduced strength. When the needle encounters the post during refilling of the cartridge, the post and the annular recessed portion of the flange separate from the plug to uncover the port. This again allows the needle access to the cavity for refilling the cavity with ink.
According to a third embodiment barrier, the previously mentioned plug comprises a hollow U-shaped portion extending into and covering the port. The U-shaped portion is capable of being pierced therethrough by the needle, as the needle encounters the U-shaped portion, to allow refilling of the cavity with ink.
According to a fourth embodiment barrier, the previously mentioned plug comprises a ball sized to be sealingly received in the port. When the needle encounters the ball during refilling of the cartridge, the ball is dislodged from the port for uncovering the port. This again allows the needle to refill the cavity with ink.
According to a fifth embodiment barrier, a flap has a first portion thereof affixed to the wall of the cartridge shell and a second portion thereof that is movable from a first position covering the port to a second position uncovering the port. A piston is connected to the second portion of the flap and extends into the port. The piston is capable of being pushed by the needle during the refilling process, so that the piston moves as the needle pushes the piston. As the needle pushes the piston, the second portion of the flap moves to the second position thereof to uncover the port.
A feature of the present invention is the provision of a barrier interposed between the cavity and the septum for isolating the cavity from the septum.
An advantage of the present invention is that use thereof prevents formation of zinc stearate crystals in the ink ejection orifices.
Another advantage of the present invention is that risk of image artifacts on a recording medium is reduced.
A further advantage of the present invention is that design freedom is increased when selecting a material for the septum.